I've read up some more on this and have gotten mine to work. This isn't exactly a cut and dry answer like would be nice, but these are the steps I did. Most of them did nothing, but I'm including them just in case something happened behind the scenes.
I first tried my
https://mobile.scottrade.com with settings as-is. Still could not get in.
I then cleared out IE's Temporary Files, Cookies, and History (open IE, select Menu, select Memory, then clear out each one by one). Could not get into Scottrade still.
I read to try through a passthrough connection, so I tried that. I hooked up the ActiveSync cable to a PC w/ Internet access. Changed my Internet connection to "pass through connector" (Programs, Settings, Data Connections, Internet Connection). Tried my website again, still no-go.
Prior to this, I had the above-mentioned Internet access set to "Automatic". All other Internet sites worked fine, so I had no reason to suspect it as the culprit. I went ahead and forced it to point to my "T Zones" GPRS entry (like the one you've called "T-Zones GPRS"). At that point, I was able to get in.
Again, I'm making no claim of finding a fix-all here. Could just be a total fluke that it started working for me! I certainly can't explain it if it actually DID fix it through anything I did, but still.... Wanted to share in case it did.
Good luck!
-Jason